Field of the Invention
The present invention relates to a Machine-to-Machine (M2M) communication method in a Heterogeneous Network (HetNet) environment and, more particularly, to a method of controlling the resources and power of a Base Station (BS) for M2M communication in an HetNet environment.
Discussion of the Related Art
In a next-generation network, Machine-to-Machine (M2M) communication has been in the spotlight as an important technology capable of creating new services. M2M communication is characterized in that communication between devices is performed in such a manner that control of a user has been minimized unlike in existing communication by a user. Such an M2M characteristic may be applied to various applications, such as a sensor device for measuring electricity and the amount of water used, a wearable device capable of checking the physical state of a user, and a logistics system. As surrounding common things become capable of wireless communication, it is expected that M2M communication devices will be deployed on a large scale.
In line with such a trend, a Machine Type Communication (MTC) device which is different from an existing cellular device and becomes the subject of M2M communication has been defined in Long Term Evolution (LTE). Furthermore, there has been defined a Random Access CHannel (RACH) process performed by MTC devices (hereinafter called devices) in a Physical Random Access CHannel (PRACH) allocated by a BS for communication.
FIG. 1 is a diagram showing an example of the allocation or a PRACH of the uplink frequency resources of a BS.
Referring to FIG. 1, in Frequency Division Duplexing (FDD) LTE, uplink resources include Physical Uplink Control CHannels (PUCCHs) and a Physical Uplink Shared CHannel (PUSCH). A frame having a length of 10 ms includes 10 subframes of 1 ms in length. In this case, a PRACH may be allocated to 0.5, 1, 2, 3, 5, and 10 subframes within a single frame. In FIG. 1, a PRACH has been allocated to two subframes.
FIG. 2 is a diagram showing an RACH process (random access process) performed by a device.
Referring to FIG. 2, for random access, a device selects one of 64 preambles in a PRACH and sends the selected preamble at step S210. In this case, if two or more devices 202 send the same preamble in the same PRACH, a collision occurs. After the preamble transmission, a BS 204 sends a Random Access Response (RAR) and schedules the devices that corresponding to successfully received preambles at step S220. In this case, the BS 204 may include an eNodeB for mobile communication, such as 3GPP, LTE, LTE-A, or WIBRO, such as a NodeB. The device 202 performs data transmission in the scheduled resources at step S230. In response thereto, the BS 204 sends a contention resolution to the device 202 at step S240.
In a next-generation network along with M2M communication, a HetNet which assists a shadow area that is difficult to be served by an existing BS due to the installation of small BS and which may distribute a load has been in the spotlight. In a HetNet, a pico BS, that is, a small BS type providing service to a relatively small area compared to a macro BS, that is, an existing BS, coexists and operates. In this case, the small BS may be called a small cell BS and may include a femto BS and a micro BS in addition to a pico BS. That is, although a small BS is hereinafter described as only a pico cell, it may be easily understood that the small BS can be applied to a femto cell and a microcell.
In the introduced conventional technologies, there are problems in that a pico BS in a HetNet does not have an algorithm for distributing a load by taking into consideration the amount of access of surrounding devices after the pico BS is installed other than the distribution of a load, a fixed value is allocated to the number of PRACHs allocated by a BS for random access, and proper scheduling is not performed on the surrounding devices of a pico BS because the amount of access of surrounding devices is not variably handled.